Transmission system for highfrequency currents



L. GOLDSTETN ET AL TRANSMISSION SYSTEMS FOR HIGH-FREQUENCY CURRENTS 3 Sheets-Sheet 1 June 26, 1951 Filed 001:. 21, 1547' 1 49 v v Q l I I $2 50 J3 INVENTORS 51 1407514; 00.40.5210 v A/flTH/M/ll-Z A. aux/av BY A TIER/V54 June 26, 1951 L. GOLDSTEIN ETAL TRANSMISSION SYSTEMS FOR HIGH-FREQUENCY CURRENTS,

Filed Oct. 21, 1947 3 Sheets-Sheet 2 5 k k a v Q s Q m E i -&

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Filed Oct. 21, 1947 3 Sheets-Sheet 3 0 m c N To P mw 0 4 7 3- mam 7 M A Patented June 26, 1951 UNITED STATES PATENT OFFICE TRANSMISSION SYSTEM FOR HIGH- FREQUENCY CURRENTS Ladislas 'Golds't'ei'n, New ra and Nathaniel L. -Ohen,- Rockaway Beach; N. Y., a'ssignors to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application October 21, 1947, Serial No. 781,174

mission control, as, for example, in the provision of such devices to effect a variation in radiated energy by varying the ionization of a gas volume in the path of such radiation in accordance with a signal. They have also been used as switching elements in transmitter-receiver arrangements wherein the gas discharge in such a device effected by the transmitted energy suffices to lgnite the device and thus tune an impedance transformer to block the line leading to the receiver.

In all these proposed systems, however, use has been made primarily of the conduction path of an ionized gas and not with the free electrons within the so-called gas plasma.

It is an object of our invention to provide a control device for high frequency energy transmission utilizing the gas plasma properties.

Another object of the invention is to provide a gaseous discharge device which may be used to control high frequency energy by the variation of the gas plasma properties of the device.

Still another object of the invention is to provide a transmission line incorporating a gaseous discharge device, as referred to above, for controlling the energy passing through said line.

The invention comprises a gaseous discharge device containing a non-electronegative gas at a pressure at which a gas discharge plasma may be established incorporated in a transmission line so that ionization of the gas Will change the characteristics of the line and therefore control the energy passing'therethrough. The invention con templates the use of such a tube to vary the conductive and dielectric characteristic of a transmission line.

The above mentioned and other features and objects of this invention and the manner of at"- tending them will become more apparent, and the invention itself will be best understod by reference to the following description of several embodiments of the invention taken in conjunction with-the accompanying drawings in which:

Figural is a structure representation of a coaxial line incorporating the discharge device of the invention;

Figure 2 is a structure representation of a modified form of the discharge device and coaxial line of Figure 1, showing the cathode and the discharge device outside of the coaxial line;

Figure 3 is'a structure representation of a portion of the arrangement of Figure 2 showing a modified cathode structure for the discharge device;

Figure 4 is a structure representation of a transmission system in which a discharge device is used to phase=modulate a high frequency current by varying the dielectric characteristic of a coaxial line;

Figure 5 is a graph illustrating the operation of the discharge device of the invention; and

Figure 6 is a graph'used to illustrate the preferable pressures used in the discharge device.

We have discovered that the conductivity of very high frequency energy through gas dis charges may be controlled by the use of a particular gas or type of gases at certain predetermined pressures ionized to current densities within certain predetermined limits. We have found that the conditions with respect to the level of the high frequency energy necessary for effecting this control are: (1) that the high frequency energy be'insu'fficient to accelerate the electrons producedin the discharge so as to produce inelastic collision of the electrons, and (2) that the meanfree path of electrons in the discharge be large compared to the" amplitude and possible electronic oscillations in the radio frequency field. Theoretical considerations lead in the case of the steady discharge to the use of non-electronegative gases and particularly to the heavier rare gases, such as, argon, neon, or krypton", or mixtures of such gases at pressures such that the electronic mean free time be of the order of the period of the high frequency energy.

The resistance oft-he cathode fall space of a gaseous discharge device to high frequency energy in the region immediately adjacent the cathode is've'r'y' high compared with the resistanc of th'e' positivecolumn and therefore where this r egio'ii'is incorporated in the'conduct ive path for the high frequency current We provide means fdr'bridg ifig this region wa'h a connector-fer the high fr ency H i g l is showiiischematically one'einbodi 'r-nentofthe in'vention'in which the discharge device is incorporated as a part of a coaxial line where the ionizable gas forms a dielectric gap in the inner conductor of the line when no discharge takes place. The coaxial line is shown provided with an outer conductor 1 and an inner concentric conductor 2 which is formed of a metal tube having a gap 3 therein. The discharge device comprises an envelope d which is made of glass and is positioned in the gap 3. The envelope 4 is tubular and has substantially the same inner diameter as the outer diameter of the inner conductor 2. A cathode 5 is provided in one end of the envelope 4 and an anode 6 is provided in the other end, these electrodes being connected, respectively, by means of wires 1 and 8 to a source of ionizing current, as, for instance, the battery 5, through a switch in.

A metal cap H is provided at the cathode and of the envelope 4, which cap forms the closure for that end of the envelope and is shaped to fit into the tubular inner conductor 2 and arranged to make an electrical contact therewith. A can i2 is provided at the anode end of the envelope 4, and forms a closure for this end of the envelope, this cap being shaped to fit into the other portion of the inner conductor 2 of the coaxial line and to make electrical connection therewith. Both cathode and anode, or at least one of them, is insulated from the associated cap since both caps are connected to the inner conductor of the coaxial line.

The envelope 4, as has already been stated, is provided with a non-electronegative gas. We have found that gases, such as argon, neon, kryp ton, xenon, helium, hydrogen and nitrogen of high purity may be used in the envelope 4, or mixtures of these gases may be used. We have found however that the heavier, rarer, gases, such as argon, neon and krypton are preferable, and

of these gases argon and krypton appear to give the best results. The gas or mixture of gases is provided at a pressure between 1 and 7 millimeters of mercury, although. pressures of 3 or 4 millimeters are preferred.

The cap I I on the cathode end of the envelope l is provided with a long enough skirt to bridge the cathode fall space or dark space in the region immediately adjacent the cathode, so that the high frequency currents will not pass through this space but will pass into the gas in the positive column thereof. The cap l2 may also be provided with a skirt which is spaced from the anode 6 but such spacing is not necessary at this end of the tube.

In order to and the flow of high frequency energy between the gas and the portions of the .inner conductor tube we preferably provide grids l3 and I4, respectively connected to caps H and I2 and extending across the ends within the envelope 4, as indicated.

In order to illustrate the operation of the arrangement of Figure 1, attention is drawn to the graph of Fig. 5. Here two representative curves are shown plotted with current in milliamperes in a logarithmic scale as the abscissae and attenuation in decibels as the ordinates. Curve l3 was made with a discharge device containing a neon gas at a pressure of 4.5 millimeters of mercury, while curve H5 was made with a discharge device containing argon at a pressure of 1.5 millimeters of mercury. The high frequency energy had a frequency of approximately 2,000 megacycles. The distance between the anode and cathode in the discharge device was chosen so that the attenuation with zero current was approximately 40 decibels. Then as the current increases it will be seen that in both cases the attenuation increases up to 15 or 20 milliamperes and then sharply decreases to approximately milliamperes where it appears to become asymptotic. By adjusting the amount of direct current for ionizing the gas it will be seen that the discharge device may be operated on the straight portion of the curve or at either bend thereof to obtain the desired control of the high frequency energy.

To illustrate the effect of the gas pressures, attention is drawn to Fig. 6 where pressures in millimeters of mercury are plotted as the abscissa against transmission in decibels as the ordinate. Three typical curves are shown, all made with argon as the gas. Curve it shows the transmission obtained at a constant ionizing current of 100 milliamperes; curve 18 shows the transmission obtained at a constant ionizing current of 50 milliamperes; and curve 19 shows the transmission obtained at a constant ionizing current of 20 milliamperes. It will be seen that the highest transmission is obtained in the 1 to 7 millimeter pressure region.

In Figure 2 is shown an arrangement whereby the cathode fall space is placed outside of the path of the high frequency energy so that no special arrangement need be provided for preventing the high frequency energy from passing through this region, so that a oath-ode of greater capability may be used. In this arangement a coaxial line is schematically illustrated, having an outer conductor 20 and an inner conductor 2|. The inner conductor 2! terminates at a distance somewhat greater than a quarter Wavelength of the high frequency energy from the end of the outer conductor.

The discharge device 22 is provided with a long t ibular glass portion 23 having a short section 24 of glass at its end and separated from its end by a metal sleeve 25 which is fused to both the portion 23 and the section 24. The other end of the section 24 is closed by a metal cap 26 which is fused to the glass thereof and is of such shape that it will fit into the end of the tubular inner conductor .2! and make a good electrical contact therewith. This cap 28 acts as the anode.

The section 2 1 has an inside diameter approximately the same as the outer diameter of the inner conductor 2!, while the portion 23 has a smaller diameter for a purpose which will later appear. The other end of the discharge device 22 extends out of the open end of the outer conductor 26 and may be provided with an enlarged portion 26 containing the cold cathode 27 which is provided with the conductor 28 for making a suitable connection to the negative terminal of a source of ionizing potential indicated at 29. The inner conductor 2i is connected by means of a wire 38 to the positive terminal of the source of ionizing potential, indicated at 3:.

A metallic sleeve 32 of the same outer diameter as that of the inner conductor 2! is provided around the tubular portion 23 of the discharge device and forms a continuation of the inner conductor 2 i and is electrically connected to the sleeve 25. This sleeve extends to the end of the outer conductor 28. This end of the outer conductor has a portion as reduced in diameter and enclosing a by pass collar 34 of insulating material which is a quarter wave length of the operating frequency long and provides a short circuit for the end of the coaxial line to pre- 'atunoei vent high frequency energy from passing out of that end.

A second coaxial line having an outer conductor 35 and an inner conductor 35 is connected to the coaxial line 2Ei2i adjacent the end thereof with the inner conductor 35 electrically connected to the sleeve 32 at a point one quarter wave length of the operating high frequency from the point on the outer conductor 2:] where the reduced diameter portion 33 begins.

Thus arranged high frequency energy can flow from one of the coaxial lines to the other without interruption although it must flow through the section 2 of the gaseous discharge device between the inner conductor 2! and the sleeve 32. A grid 3? may be placed in the envelope of the discharge device at the inner end of the portion 23 and attached to the sleeve 25 to aid the flow of energy between the gas in the section 2 and the sleeve 32.

In the arrangement just described the high frequency current passes only through that portion of the gas provided by the section 2 between the inner conductor 2? and the sleeve 32. The gas used in the device and the pressures employed are similar to those already described.

The arrangement of Figure 2 shows a cold cathode in the discharge device 22. It will be evident however that a heated cathode may be used and such an arrangement is shown in Figure 3. Here the parts are the same as in Figure 2 except that a cup shaped cathode 38 is heated by means of a filamentary heater 39 in a manner well known in the art.

In some instances it may be desired to use discharge devices similar to those already described for changing the dielectric characteristics of a transmission line in order to vary the phase of high frequency energy passing therethrough and our invention is intended to cover the use of the discharge devices already described for such purposes. One embodiment of an arrangement for using the discharge device in this manner is illustrated in Figure 4. A constant ultra high frequency source 49 is connected through a coaxial line 4! to a suitable radiating antenna 42. In the coaxial line is provided a discharge device 43 formed of an annular envelope which surrounds the inner conductor id of the coaxial line M. This annular envelope may be provided at its ends with annular cathode and anode, so disposed that they will not interfere with the passage of high frequency energy, as will be understood, these being connected respectively by conductors 45 and 46 to a battery 4! through'a variable resistance 48 and the secondary 39 .of a transformer 58, the battery ill and resistance 48 being bridged by a condenser 5!. The primary 52 of. the transformer 50 may be connected to a. suitable audio amplifier 53 controlled by a. microphone 54. Excitation of the microphone 54 will produce variations in the ionizing currents for the discharge device thus changing the dielectric constant at the signal frequency and thereby modulating the high frequency energy delivered to the antenna 42.

It will thus be seen that we have provided a discharge device and a system incorporating it for varying ultra-high frequency energy which is simple to construct and easy to control and operate.

While we have described devices using direct current for producing the ionization, we have found that alternating currents are equally suitable, as long as the required plasma conchtions are obtained. The principles of our invention have been set forth above in connection with certain specific apparatus. t is to be clearly understood, however, that this description is made only by way of example and not as a limitation of the scope of our invention.

What is claimed is:

1. A transmission control system for the control of high frequency currents having certain amplitudes and periods comprising coaxially disposed outer and inner conductors for conducting said currents, a container having at least a portion thereof made of insulating material and forming a portion of said inner conductor, an ionizable gas within said container, electrical means independent of said high frequency currents to ionize said gas, the mean free path of electrons in said gas being large compared to the amplitudes of the high frequency currents, the electronic mean free time being of the order of the period of the said high frequency currents, energy of said high frequency currents under control being insufiicient to accelerate electrons in the gas to inelastic collision levels, said electrical means to ionize said gas including means mounted in said container to produce an electron current substantially coaxially of said conductors.

2. A transmission control system according to claim 1, in which the gas is a non-electronegative gas.

3. A transmission control system according to claim 2, in which the gas comprises one of the gases argon, neon, krypton, xenon, helium, hydrogen, nitrogen, or mixtures thereof.

4. A transmission control system according to claim 1, in which the gas comprises a non-electronegative gas at a low pressure at which a gas discharge plasma may be established.

5. A transmission control system for the control of ultra high frequency currents comprising a conductor for conducting said currents, a container having at least a portion thereof made of insulating material and forming a portion of said conductor, an ionizable gas Within said container, electrical means independent of said high frequency currents mounted in said container to produce an electron current parallel to said conductor to ionize said gas, said means to ionize said gas to produce a positive column, the attenuation of ultra high frequency currents passing through said gas being determined by the value of said ionizing current through said positive column.

6. A transmission control system according to claim 5, in which said gas has a pressure at which a gas discharge plasma may be established.

'7. A transmissioncontrol system according to claim 5, in which said gas is one of the gases argon, neon, krypton, xenon, helium, hydrogen, nitrogen, or mixtures thereof and the pressure is between 1 and 7 millimeters of mercury.

8. A transmission control system for controlling ultra-high frequency currents comprising a coaxial transmission line, a gas discharge device having an envelope and an ionizable gas within said envelope at a pressure at which a gas discharge plasma may be established, said envelope being positioned in series in a portion of one of the conductors of said transmission line, and means for passing a current through said gas, said current passing means being mounted parallel to said transmission line.

9. A transmission control system according to gamer claim 8, in which the gas is a non-electronegative gas.

10. A transmission control system according to claim 9, in which the gas is one of the gases argon, neon, krypton, Xenon, helium, hydrogen, nitrogen, or mixtures thereof.

11. A transmission control system comprising a gas tube having a cathode and an anode and enclosing a non-electronegative gas within a given pressure zone, an electric current source, means for adjustably coupling said source between said cathode and anode to effect produc- .tion of a gas plasma within said tube, means for coupling a high frequency conductor across the normal cathode-fall space of said gas plasma Within said tube, and means for connecting said gas tube in series with a conductor of an ultrahigh frequency transmission line.

12. A transmission control system according to claim 11, in which the pressure of the gas is between 1 and 7 millimeters of mercury.

13. A transmission control system according to claim 12, in which the gas is one of the gases argon, neon, krypton, .zenon, helium, hydrogen, nitrogen, or mixtures thereof.

14. A transmission control system ior the control of ultra-high frequency currents compris ing an outer tubular conductor and an inner concentric conductor, a container forming a portion of one of said conductors, an ionizable gas within said container having a pressure at which a gas discharge plasma may be established, and means for controlling the ionization of said gas.

15. A transmission control system according to claim 14, in which the container forms a portion of the inner concentric conductor.

16. A transmission control system for the control of ultra-high frequency currents comprising a first coaxial line having an outer conductor and an inner conductor, said inner conductor terminating short of the end of said outer conductor, a gaseous discharge device having a tubular envelope with an anode and a cathode at opposite ends thereof, said envelope for a portion of its length adjacent said anode having a diameter substantially equal to the diameter of said inner conductor, the anode end of said envelope being positioned within said outer conductor so as to form a continuation of said inner conductor with said anode electrically connected to said inner conductor, said cathode end of said envelope extending out of the end of said outer conductor a second coaxial line connected to said first coaxial line at a point spaced from the end thereof, a metallic sleeve surrounding said envelope from a point spaced from the anode end thereof to the outer end of said outer conductor and forming a continuation of said inner conductor of said first coaxial line the inner conductor of said second coaxial line being connected to said sleeve at a point approximately one quarter wave length of the operating frequency from the end or" the outer conductor of said first coaxial line, means for substantially shorting the end or" said first coaxial line with respect to the ultra-high frequency currents a source of potential for ionizing the gas in said device, means for connecting the negative termina-l of said source to said cathode and means including said inner conductor of said first coaxial line for connecting the positive terminal of said source to said anode.

17. A transmission control system according to claim 16, in which the gas is a non-electronegative gas at a pressure between 1 and 7 mil-- limeters of mercury.

18. A transmission control system according to claim 5, in which the inner surface of the portion of said container forming a portion of said conductor is coated with a photo-conductive material.

19. An electron discharge device comprising an envelope, a non-electronegative gas within said envelope at a pressure between 1 and '7 millimeters of mercury, an anode within said envelope, a cathode within said envelope spaced from said anode, and electrical connections for said anode and cathode respectively leading outside said envelope.

20. A system for phase modulation of ultrahigh frequency currents comprising a coaxial line having an outer conductor and an inner concentric conductor, a gaseous discharge device having an annular envelope mounted in said line, and an ionizing gas Within said envelope and an anode and a cathode mounted to produce an electron current parallel to said coaxial line Within said envelope, means to apply a potential to said anode and cathode for causing ionization or said gas, said ionization causing means being designed to produce a positive column, and means for varying said potential in accordance with a signal.

21. A transmission control system for the control of high frequency currents having certain amplitudes and periods comprising means defining a path for said high frequency currents, a container having at least a portion thereof made of insulating material and located in said path, an ionizable gas within said container, electrical means independent of said high frequency currents mounted to ionize said case to produce a positive column in said container parallel to said path of said ultra high frequency currents, the mean free path of electrons in said gas being large compared to the amplitudes of the high frequency currents, the electronic mean free time being of the order of the periods of said high frequency currents, energy of said high frequency currents under control being insufiicient to ac-- celerate electrons in the gas to inelastic collision levels.

LADISLAS GOLDSTEIN. NATHANIEL L. COHEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,106,770 Southworth et a1. Feb. 1, 1932 2,412,892 Krasik Dec. 17, 1946 2,413,963 Fiske et a1. Jan. '7, 1947 2,416,168 Fiske Feb. 18, 1947 

